1. Field of the Invention
The present invention relates to an ultrasonic probe to be used in an ultrasonic diagnosis apparatus or an ultrasonic endoscope, and in particular to an ultrasonic probe adapted to prevent an adhesive, which is used in manufacturing the ultrasonic probe, from protruding to an electrode portion and damaging the electric connection.
2. Description of a Related Art
In medical fields, various imaging technologies have been developed in order to observe the interior of an object to be inspected and perform diagnosis. In particular, ultrasonic imaging for acquiring internal information of the object by transmitting and receiving ultrasonic waves has been utilized in a wide range of departments including not only the fetal diagnosis in the obstetrics, but also gynecology, circulatory system, digestive system, and so on, as a safe imaging technology enabling image observation in real time and accompanying no exposure to radiation.
The ultrasonic imaging is an image generation technology utilizing the nature of ultrasonic waves that the ultrasonic waves are reflected at a boundary between regions with different acoustic impedances. An ultrasonic diagnosis apparatus utilizing the ultrasonic imaging is provided with an ultrasonic probe to be used in contact with an object to be inspected, or an ultrasonic probe to be used by being inserted into an abdominal cavity of the object. Moreover, an ultrasonic endoscope comprising a combination of an endoscope for optically observing the interior of the object and an ultrasonic probe for intracavity has been also used.
As an ultrasonic transducer for transmitting and receiving ultrasonic waves in the ultrasonic probe, a piezoelectric vibrator having electrodes formed on both ends of a piezoelectric material is usually used. When a voltage is applied to the electrodes of the vibrator, the piezoelectric material expands and contracts to generate ultrasonic waves. Furthermore, a plurality of vibrators are one-dimensionally or two-dimensionally arranged and driven by drive signals with a predetermined delay given thereto, and thereby, an ultrasonic beam can be formed toward a desired direction. On the other hand, the vibrators expand and contract by receiving propagating ultrasonic waves to generate electric signals. These electric signals are used as reception signals of the ultrasonic waves.
In particular, in the ultrasonic probe to be used by being inserted into an abdominal cavity, there is a need to narrow and soften an insertion tube for feeding the ultrasonic probe to near an affected part and also to miniaturize constituent elements arranged at the tip part of the insertion tube.
FIG. 11 is a cross sectional view showing an internal structure of a conventional ultrasonic probe. A vibrator comprises a piezoelectric material, and upper and lower electrodes which are formed in the upper and lower sides of the piezoelectric material by coating. A backing material is provided on one surface of the vibrator, while on the other surface, an acoustic lens is provided via an acoustic matching layer. The vibrator and the backing material are bonded to each other with an adhesive such as an epoxy resin.
FIG. 12 is an enlarged view of a portion “A” of FIG. 11, and shows the adhesive flowing to the side portion of the vibrator and the backing material. The flow of the adhesive occurs by pressing the vibrator and the backing material when bonding and fixing the both to each other. This pressing eliminates mixing of a foreign matter such as air and enables uniform bonding. However, the adhesive may protrude to the side portion and cover the electrode due to the pressing. In this case, even if wiring electrodes such as lead wires or a FPC (flexible printed circuit board), which transfer signals from a drive unit, are provided, electrical coupling cannot be obtained between the wiring electrode and the electrode of the vibrator. It is therefore necessary to make electric connection after removing the adhesive, or to reject such an ultrasonic probe as a defective one.
Japanese Patent Application Publication JP-A-8-79894 discloses an ultrasonic probe capable of preventing an adhesive from flowing to the periphery. According to JP-A-8-79894, as shown in FIG. 13, a groove for retaining the adhesive therein is provided in a peripheral portion of a backing material so as to lead the adhesive, which has overflowed when bonding the backing material and the electrode surface to each other, into the groove. This can prevent the adhesive from flowing to the periphery. Moreover, JP-A-8-79894 describes that if especially the distance between the groove and the edge of the backing material, the groove width, and the groove depth are set to a half of a wavelength of an ultrasonic wave, then the sound absorptivity is not to be degraded even if the adhesive fills in this groove and is solidified therein.
By the way, in order to fabricate a convex-type ultrasonic probe, a plurality of vibrators (piezoelectric elements) needs to be arranged as an array on the curved surface of a cylindrical backing material, for example. However, it is difficult to prepare the piezoelectric elements one by one, and then arrange a plurality of piezoelectric elements at fixed intervals in a primary arranging direction (azimuth direction) on the cylindrical curved surface, and bond and fix them. Then, as shown in FIGS. 14A-14C, there is used a technology of manufacturing an ultrasonic probe by utilizing a thin and tabular auxiliary member (also referred to as a “thin backing material”) formed of a backing material and having flexibility. First, a tabular piezoelectric element is bonded onto the auxiliary member. Then, the tabular piezoelectric element is cut in an elevation direction, which is perpendicular to the azimuth direction, and divided to arrange a plurality of piezoelectric elements in an array on the auxiliary member (FIG. 14A). The auxiliary member, on which the plurality of piezoelectric elements are arranged, is bonded onto the curved surface of the cylindrical backing material by using an adhesive (FIG. 14B). As a result, an array of elements at fixed intervals can be achieved (FIG. 14C). As the size of the ultrasonic probe is reduced, the arrangement of the piezoelectric elements one by one becomes a finer and more precise task, and therefore, this technology is effective.
In the conventional ultrasonic probe, although the width (length in the elevation direction perpendicular to the azimuth direction) of the cylindrical backing material is usually larger than that of the thin backing material, both widths are becoming equal to each other as the size of the ultrasonic probe itself is reduced. Consequently, the protrusion of the adhesive in bonding the thin backing material to the cylindrical backing material has been a problem in manufacturing the ultrasonic probe. Namely, if the amount of the adhesive used in bonding the thin backing material to the cylindrical backing material is insufficient, the sound absorption effect of the backing material cannot be sufficiently obtained, which adversely affects the acoustic performance of the finished ultrasonic probe. On the other hand, if the adhesive is used in excess, then the adhesive is likely to protrude because the ultrasonic probe is small, which leads to a problem that the side face is covered with the adhesive as shown in FIG. 14C. In particular, if the protruded adhesive climbs up the piezoelectric element side above the bonding surface, i.e., the side face of the thin backing material or the piezoelectric elements, then the side face may be covered with the adhesive to cause failure of electric connection because this is the place where the wiring electrode for transferring the electric signal from the drive unit and the electrode of the piezoelectric element are electrically connected to each other later.
FIG. 15 is an assembly view of a convex-type ultrasonic probe formed with an adhesive retaining groove directly under a piezoelectric element. In the ultrasonic probe as shown in FIG. 15, the groove for retaining the adhesive therein as taught in JP-A-8-79894 is applied to the convex-type ultrasonic probe. The adhesive retaining groove is formed within a curved surface of a cylindrical backing material, to which a thin backing material having a piezoelectric element array mounted thereon is bonded. The adhesive retaining groove is formed in the azimuth direction at the position close to the side edge in the bonding surface.
Moreover, Japanese Patent Application Publication JP-A-7-236638 discloses that, as shown in FIG. 16, vibrators are fixed to an auxiliary member formed of a backing material, and an auxiliary-member fitting groove and drain ditches for allowing an excess adhesive to escape therein are provided in a fixation material formed of a backing material in advance. Since the fitting groove having the same width as that of the vibrator is formed in the fixation material, the alignment between the auxiliary member having the vibrator mounted thereon and the fixation material can be automatically achieved when the auxiliary member is fitted into the fitting groove of the fixation material. Furthermore, the adhesive-escaping drain ditches, which are formed in the azimuth direction at both ends of the fitting groove, prevent an excess adhesive from protruding. In addition, in the fixation material, a chamfered surface is formed in a curved portion such that the bending angle of an FPC for leading wirings from piezoelectric elements is devised to be relaxed so as not to cause damages such as disconnection.
The above-described conventional examples prevent the adhesive from protruding to the side face, thereby preventing the electrode of the piezoelectric element from being isolated from the wiring electrode. However, in both examples, the drain ditch, into which the adhesive escapes, is positioned directly under the piezoelectric element, and therefore, an adhesive layer, which is partially thick by the amount of the width of the groove, is formed in the vibration direction of the piezoelectric element. Since the sound attenuation capability of the adhesive is small as compared with that of the backing material, the thick adhesive layer formed in the groove directly under the piezoelectric element will degrade the performance of the probe. Moreover, if a bubble enters the groove, an air region will be included between the piezoelectric element and the backing material, which has a more unfavorable effect on the acoustic performance of the ultrasonic probe.
On the other hand, if the volume of the drain ditch is small, the adhesive that has not been stored into the groove will protrude to the side face, which may consequently cause failure of electric connection between an electrode of the piezoelectric element and the wiring electrode for transferring a signal from the drive unit, as is conventional. Since a length in the elevation direction has been reduced as advances have been made in miniaturizing the ultrasonic probe, the area causing an acoustic loss is required to be reduced as much as possible. Therefore, it is, of course, better that there is no thick adhesive layer stuck in the groove directly under the piezoelectric element.